1. Field of the Invention
The present invention relates generally to a digital signal composing circuit and more particularly is directed to a digital signal composing circuit which is suitable for being used in smoothly connecting or mixing a plurality of digital information signals.
2. Description of the Prior Art
In a scrambling system for audio frequency signals and so on in which an audio signal, for example, is divided into blocks, each block being formed of a plurality of segments, the plurality of segments are rearranged on a timebase in a predetermined order at every block and upon reception, these segments are re-arranged in the original arrangement order to restore the original audio signal, if a system such as a VTR (video tape recorder) and the like having a timebase fluctuation exists in the transmission path thereof, when these segments are rearranged at the receiving side, the connected portion between the ends of the segments is displaced so that the original audio signal is distorted, a noise is superimposed upon the original audio signal and so on, thus the quality of the audio signal being deteriorated.
Therefore, as a method for solving the above problem, there is proposed a so-called cross-fade signal processing system in which as, for example, shown in FIG. 1, when digital data X and Y having different contents A and B are connected to each other, near the connection point, one digital data X is gradually decreased in level, while the other digital data Y is gradually increased in level over a predetermined interval (cross-fade period) t so as to connect both the data with each other smoothly.
By the way, a conventional circuit employing such cross-fade signal processing system requires a multiplier to apply the cross-fade so that the construction of the circuitry becomes large in structure. Particularly when this circuit is formed as an IC (integrated circuit), the manufacturing cost thereof is greatly affected so that the circuit becomes very expensive.